This Recommendation provides a framework for multicast based IPTV content delivery based upon different content delivery functional models and their associated requirements for delivery of IPTV content to multiple end-users simultaneously. The content delivery functional models are defined according to different methods of multicastbased IPTV content delivery in terms of the common functions of the IPTV functional architectural approaches (i.e.@ Non-NGN@ NGN-non-IMS@ and NGN-IMS) described in [ITU-T Y.1910]. For each content delivery functional model@ different roles for the functions of the IPTV architecture are identified according to the multicast capabilities defined in [ITU-T Y.2236]. For each multicast capability@ the corresponding requirements for multicast based IPTV content delivery are further identified based on the requirements to support IPTV services [ITU-T Y.1901].